1. Field of the Invention
The present invention relates to ceramic electronic components, and more particularly, to ceramic electronic components having a high level of reliability in terms of thermal shock resistance and flexural strength.
2. Description of the Related Art
In general, electronic components using ceramic materials, such as capacitors, inductors, piezoelectric devices, varistors, or thermistors, include a ceramic sintered body made of ceramic materials, internal electrodes formed inside the ceramic sintered body, and external electrodes formed on the surfaces of the ceramic sintered body to be connected to the internal electrodes.
A multi-layer chip capacitor (hereinafter, also referred to as “MLCC”) among ceramic electronic components includes a plurality of layered dielectric layers, internal electrodes disposed to face each other in which each pair of internal electrodes has one of the dielectric layers disposed therebetween, and external electrodes electrically connected to the internal electrodes.
The MLCC provides the advantages of compactness, high capacitance, and ease of mounting, so it is therefore used extensively in mobile communications devices such as computers, PDAs, and cellular phones.
The MLCC, when used, is mounted on a circuit board. More specifically, as shown in FIG. 1, a circuit board 1 has conductive lands 2 and 3 formed thereupon and the conductive lands 2 and 3 have solder fillets 4 and 5 respectively formed thereupon by soldering. Through the solder fillets 4 and 5, external electrodes 7 and 8 of a multi-layer chip capacitor 6 are electrically connected to the conductive lands 2 and 3, respectively.
When the MLCC is mounted on the circuit board by soldering and the circuit board is cut, thermal shock and shear stress are transmitted to the MLCC. When the thermal shock and the shear stress are transmitted, a crack may occur in the MLCC. The external and internal electrodes of the MLCC are easily shrunken and expanded, relative to ceramic materials. These shrinkage and expansion stresses are concentrated at the interface between the external electrodes and ceramic layers, whereby a crack may occur at the interface between the external electrodes and the ceramic layers. Also, the warping of the circuit board may cause a crack on the mounting area of the MLCC and at the interface between the external electrodes and the ceramic layers.
A circuit board, upon which the MLCC is mounted, is applicable to industries such as the airline industry, the automotive industry, and the consumer electronics industry. When a variation in temperature is transferred to such a circuit board, the stress caused by warpage or thermal shock is transmitted to the interface between the external electrodes and the ceramic layers of the MLCC, whereby a crack may occur.
When the stress is transmitted to the interface between the external electrodes and the ceramic layers, the crack starts therefrom and propagates in the body of the MLCC. The crack may be propagated toward the internal electrodes. When the crack is propagated to reach the internal electrodes, a short circuit may occur in the MLCC, thereby causing functional loss to an electronic device.
Korean Patent Laid-Open Publication No. 2006-0082671 discloses a method of improving the thermal and mechanical reliability of a multi-layer chip capacitor by ensuring that the length of external electrodes is greater than a certain predetermined measurement. However, when the MLCC manufactured by the use of such a method is mounted on a circuit board two or more times by the use of a reflow method, a crack occurs at the interface between the external electrodes and ceramic layers. Also, when a strong external force is applied to the circuit board upon which the MLCC is mounted causing it to be flexed by more than 2 mm, a crack occurs at the interface between the external electrodes and the ceramic layers of the MLCC, whereby electrostatic capacitance decreases.
U.S. Pat. No. 6,350,759 discloses that when external electrodes of a multi-layer chip capacitor are mounted on conductive lands of a circuit board, a separate metal terminal is used to reduce the occurrence of stress. The use of the additional metal terminal causes difficulties in a mounting process and problematic manufacturing of the additional element.
Therefore, there is a need for a method of developing greater mechanical reliability, considering the use environment of the MLCC, that is, a high level of reliability in terms of thermal shock resistance and flexural strength.